• Noise can be defined as disagreeable or undesired sound.• What is sound to one person may be a noise to somebody else.• The amplitude of sound waves corresponds to its Loudness and the frequency corresponds to its pitch and the waveform to the quality.• Sound of frequency 20Hz to 20000 Hz can be heard by the human ear and constitutes the audible frequency range.• To process sound the main system components required are microphones for sound input, amplifiers for boosting the loudness levels and loudspeakers for output or playback of sound.• When sound needs to be processed in a computer it should first be converted to digital format. This is done by Sampling, Quantization and code –word generation.• To compress the sound files both lossy as well as lossless compression algorithms can be used.• Example the MP3 audio format for distributing music on the Internet is based on a lossy compression algorithms.• Music generated by synthesizers are pure digital sound which do not
Power of Sound• When something vibrates in the air when it is moving back and forth it creates wave of pressure.• The waves spread like ripples from pebble tossed into a still pool and when it reaches the eardrum the change of the pressure or vibration is experienced as sound.• The sound pressure levels are measured in decibels (db).
Unit IV Audio and Video Sound – It is the result of pressure variations oroscillations in an elastic medium like air, water, solids generated by a vibrating surface or turbulent fluid flow. Sound is a form of energy capable of flowing fromone place to another through a material medium. It is generated from vibrating objects when part of the energy of vibration is converted to sound energy.
Multimedia Sound• Windows system default file format for audio is WAV which resides in the WindowsMedia subdirectory.• Macintosh systems use SND as default format for audio.
Acoustics• It is a branch of science ie physics that studies sound.• It is a wave motion in gases, liquids and solids and the effects of such wave motion.• Thus the range of acoustics ranges from physical acoustics to bioacoustics , psychoacoustics and music, design of theatres and concert halls etc.• Sound is a form of energy. It is generated from vibrating objects and can flow through a material medium from one place to another.• During the generation of sound the kinetic energy of the vibrating body is converted to sound energy.• Sound energy flowing outwards from its point of generation can be compared to spreading wave over the surface of water.
Acoustic Engineering• The application of acoustics in technology is called as acoustic engineering.• The sub divisions of acoustics are:1. Aero-acoustics – It is concerned with how gas flows produce sound and has application in aeronautics ex- Sound and shockwaves produced by jets.2. Architectural –acoustics: Concerned with the study of sound in building like halls and auditoriums.3. Bio-Acoustics: Concerned with the study of sound in medicine ex – ultra- sonography .4. Physical-acoustic: Concerned with interaction of sound with materials and fluids ex- how shock waves travel through the solid and liquid portions of the earth’s crust.5. Speech communication: It is concerned with the production, anyalysis, transmission and recognition of speech.6. Ultrasonics: Concerned with the study of high frequency sounds beyond human hearing range.7. Musical – acoustics: Concerned with the study of sound in relation to musical instruments .
Characteristic of Sound• Amplitude – it is the maximum displacement of a particle in the path of a wave and is measure of the peak-to-peak height of the wave. For sound waves amplitude mean the loudness of sound. Larger the energy of the sound wave more is its amplitude and louder will be its effect in our ears.• Wave length- The wavelength (λ) which is the distance travelled by the wave during one cycle unit of wave length is in meters.• Frequency – The frequency (f) which is the number of particle variation cycles in the medium per unit time or the number of cycles per second and is expressed in HZ.• Period – The period (T) which is the time taken for one cycle of a wave to pass a fixed point. It is related to frequency by T = 1/f sec.
• Speed/Velocity- The speed of sound propagation c, the frequency f and the wavelength, (λ) are related by the following equation: C=f λ• Waveform – This indicates the actual shape of the wave when represented pictorially. Shapes of the waves can be sinusoidal, square, triangular etc. Two sounds having the same loudness and pitch but having different waveforms give different sound in our ears.
Hearing Threshold and Masking• Two fundamental phenomena that govern human hearing are the minimum hearing threshold and amplitude masking.• Minimum threshold is the least audible sound that the normal human ear can detect and hear.• The minimum threshold values ie the amplitudes of the least audible sounds when plotted against frequency values gives rise to the minimum threshold curve.
• The upper portion denotes the audible region while the lower portion denotes the inaudible range.• The minimum value on the curve occurs around the frequency of 1 KHZ where the sensitivity of the human ear is the greatest.
• Amplitude Masking occurs because an audible sound has a tendency to distort the threshold curve and shift it upwards.• The human ears contains about 30000 hair cells which detect local vibrations and convey audio information to the brain via electrical impulses.• These hair cells respond to the strongest stimulation in their local region.• The amount of distortion of the curve is restricted to a small region surrounding the strongest sounds.• The entire range of audible frequencies is divided into a number of such regions known as critical bands.
• The critical bands are much narrower at low frequencies than at high frequencies and the width of critical band determine the extent of the distortion of the threshold curve.• Within a critical band of frequencies only the strongest sound will be heard while the others are subdued.• Sound 1 seems to distort the curve in such a way that another sound, sound 2 which would normally have been audible if it had been occurred alone , falls below the threshold curve and is rendered inaudible. Sound 1 is called the masker and sound 2 is called masked.
Temporal Masking• This occurs when tones are sounded close in time but not simultaneously.• A louder tone occurring just before a softer tone makes the latter inaudible.• Temporal making increases as time differences are reduced.• The concept of masking is used in making digital audio compressors by analyzing which portions of sound are inaudible to the average human ear and selectively discarding those portions to reduce the file size of the digital audio.
Raster Scanning• It is a rectangular pattern of image capture and reconstruction in television.• In this the scanning is done line by line which creates a raster.• It is the systematic process of covering the area progressively one line at a time.• In raster scan an image is subdivided into a sequence of strips known as “ scan lines”.• Each scan line can be transmitted in the form of an analog signal as it is read from the video source.• This ordering of pixels by rows is known as raster order or raster scan.
• Raster scanning is the pattern of image detection and reconstruction in television and is the pattern of image storage and transmission used in most computer bitmap image systems.• In raster scan an image is cut up into successive samples called pixels along scan lines.• Each scan line can be transmitted as it is read from the detector or can be stored as a row of pixels values in an array in a computer system.
• After each scan line the position of the scan line is advanced typically downward across the image in a process known as vertical scanning.• A raster is a series of adjacent parallel lines which together form an image on a display screen.
Scanning and its types• One sweep from top to bottom of screen is called as field.• Moving the beam from left to right and back is called as scanning.• There are two of scanning : 1) Interlaced scanning2) Non- Interlaced canning
Interlace Scanning• In this the scan-lines for one field are offset or delayed and interleaved with the next field.• After every other field the scan-line repeats therefore two fields are required to make a complete picture or frame.• The beam sweeps 262.5 times horizontally for each vertical sweep.• To get better picture and avoid flickering interlaced scanning is used.
Non-Interlace Scanning• The CRTs used for computers usually have non-interlace scanning.• The vertical sweep rate is 60HZ and 260 sweep lines per field .• In non-interlaced scanning there is only one sweep which sweeps from top to bottom.• Here the picture is comprised of one frame.
Sensors for Camera• The primary function of a image sensor is the conversion of light photons falling onto the image plane into a corresponding spatial distribution of electric charge.• The accumulation and storage of this charge at the point of generation and the conversion of charge to a usable voltage signal.• Sensors can be classified into two groups:1) Vacuum tube 2) Solid-state devices.
Vacuum tube• Vacuum tube devices in which the charge readout is accomplished by an electron beam sweeping across the charge in a raster fashion similar to that in a television picture tube.• Example of vacuum tubes – TV camera tube
Solid State device• It is based on charge coupled devices or photodiodes.• Examples of Solid State device – Charge Coupled Device (CCD)• There are two types of CCDs – Linear CCD - Area CCD
Vaccum Tubes – TV Camera Tubes• Vacuum tubes where the only technology available for television for many years till now.• Light from the scene is imaged by a lens onto a photoconductive target formed on the inner surface of an end window in a vacuum tube.• An electron gun is placed at the opposite end of the tube to the window , and it provides a source of electrons that are focused into a beam which is accelerated towards the target by a positive potential on a fine mesh placed just in front of the target and scanned across the target by an electrostatic or magnetic deflector system.• The target consists of a glass faceplate on the inner surface, on which is placed a transparent electrically conducting coating of indium tin oxide.• On top of this is deposited a thin layer of photoconductive material in a pattern of tiny squares, each insulated laterally from its neighbors.• The transparent coating is connected to a positive voltage through an electrical load resistor across which the signal voltage is developed.
• In the absence of light the electron beam causes the external surface of the photoconductor to be charged to near zero potential.• Light causes the resistance of the photoconductor to decrease and its surface to acquire a more positive potential due to which the accumulation of positive charge.• At each point on the surface touched by the electron beam some of the beam current is deposited to neutralize the positive charge present due to the illumination.• The rest passes through the load resistor generating an output voltage that is a function of the light intensity at that point.
CCD• CCD is another sensor. CCD is fabricated on a single crystal wafer of P –type silicon and consists of one or two dimensional array of charge storage cells on centers .• Each cell has several closely spaced electrodes ie gates on top, seperated from the silicon by an insulating layer of silicon dioxide.• The charge is stored under one of the electrodes and its location within the cell is defined by the pattern of positive voltage applied to the electrodes.• By applying a coordinated sequence of clock pulses to all the electrodes in the array, packets of stored charge are transferred from one cell to the next until they finally reach a sensing amplifier which generates a voltage signal proportional to charge.• The result is a device that has an linear variation of output voltage with light from the minimum useful level set by noise to the maximum useful level set by saturation of the output amplifier or the limited capacity of the charge storage cells.• Compared with photographic film CCDs are from 10 to 100 times more sensitive, linear in response rather than nonlinear and have a much greater dynamic range so that both faint and bright objects can be recorded in the same exposure.
Types Of CCDs• There are two types of CCDs –1) Linear Charge Coupled Devices and 2) Area Charge Coupled Device.Linear Charge Coupled Device – The Linear CCD consists of a line up to several thousand photosites and parallel CCD shift register terminated by a sensing amplifier. Each photosite is separated from a shift register cell by a transfer gate. During operation a voltage is applied to each photosite gate to create empty storage wells which then accumulate amounts of charge proportional to the integral of the light intensity over time. At the end of the desired integration period the application of a transfer pulse causes the accumulated charge packets to be transferred simultaneously to the shift register cells through the transfer gates. The charges are clocked through the shift register to the sensing amplifier at a rate up to 20 MHz, producing a sequence of voltage pulses with amplitudes proportional to the integrated light falling on the photosites. There is a limit between 105 to 106 depending on photosite size and dimensions to the number of electrons that can be stored in a particular cell beyond which electrons start to spill over into adjacent cells. The saturation charge in electrons is roughly 1000 to 2000 times the area of photosite in square micrometer.
Area Charge Coupled Devices• The Area CCDs uses three basic architectures:1) The simplest is the full-frame CCD consisting of an imaging area separated from a horizontal CCD shift register by a transfer gate.2) In the imaging area, each photosite is one stage of a vertical shift register separated from neighboring shift registers by channel stops and antiblooming structures. During the light integration period the vertical clocks are stopped creating potential wells which collect photoelectrons.3) At the end of this period the charge is clocked out vertically one row at a time into the horizontal shift register. The charge in the horizontal shift register is then very rapidly shifted towards the output amplifier by the application of horizontal clock signal.4) In the diagram of full-frame CCD which has pixels arranged in a 1024x1024 configuration and dual horizontal shift registers and outputs to achieve a 30 frame per second readout rate.5) To avoid the image sneering during the readout period full frame CCD sensors must be operated with external shutters as in digital cameras produced by most of the companies.
Color Fundamental• Within the computers the pixels are stored according to RGB color space.• There are three different ways to specify the colors ie – Hue, Saturation and Brightness which are the components of color.• Hue – It is the basic properties of what the human eye perceives as colour. It refers to the colour quality of the light and corresponds to the colour names that are used such as orange , indigo, cyan etc. When we use colour it means Hue. Other words Hue is the quality of colour.
Saturation –•It refers to the purity of light.•The more saturated the stimulus the strongerthe color experience and less saturated, themore it appears white or gray or black which arecalled achromatic or no color.Brightness –•It is the experience of intensity.
Primary and Secondary ColorsPrimary Colors –These are those colors that cannot be created bymixing other colors.There are three primary colors ie red, green andBlue.Secondary Colors –•A color created by mixing equal amounts of twoprimary colors is called a secondary color. Ex –Green+Blue=Cyan, Blue+Red=Magenta,Red+Green=Yellow
Color Mixing• There are two different ways to combine colors those are1) Additive mixing2) Subtractive mixing Additive Mixing – It refers to combining lights of two different colors. Ex – by mixing the shines of two colored spotlights on the same white wall. Additive color mixing comes about when two or more Hues mixing together to create a third Hue. The additive color model is the one ued in computer displays as the image is formed on the face of the monitor by combining beams of the green, and blue light in different proportions
Subtractive Mixing –•It describes how two colored paints or inks combine ona piece of paper.•The three subtractive primary colors are Cyan, Magentaand Yellow.•It subtracts all the wavelengths not in the color filter.That is when we put a Magenta filter in front of a light weare removing all the wave lengths that are not Magenta.Magenta is comprised of Red and Blue. So when we putthat filter it is as we were using a Red and Blue filtertogether. If we want to make Red we need to remove theBlue.•By adding Yellow to the Magenta we are in essencecanceling the Blue and leaving with Red.•Color printers use the subtractive color model and useCyan, Magenta and Yellow inks.
Color Gamut• The dyes , pigments and phosphors used to create colors on paper or computer screens are imperfect and cannot recreate the full range of visible colors.• The actual range of colors achievable by a particular device or medium is called its color gamut .• Different devices such as computer monitors, printers, scanners and photographic film all have different color gamuts, so the problem of achieving consistent color is quite challenging.• Different media also differ in their total dynamic range how dark is the darkest achievable black and how light is the brightest white.
File Formats• Audio File Formats :I. WAV(Wave Form Audio)II. MID or MIDI (Musical Instrument Digital Interface)III. AU (Audio)IV. MP3 (Mpeg Layer – III)V. VOC (Voice)VI. RMF (Rich Music Format)VII.MP3PROVIII.WMA (Windows Media Audio)IX. RA (Real Audio)X. WAV PackXI. MPC (Muse Pack)XII.MOD (Module)
• WAV (Waveform Audio) – This is the format for sampled sounds defined by Microsoft for use with Windows. It is an expandable format which supports multiple data formats and compression schemes .• AIFF (Audio Interchange File Format) – The Interchange File Format (IFF) is a generic File format developed by Electronic Arts in 1985 to facilitate data transfer between software programs of different vendors, so they don’t have any common extension. An IFF file is built up from chunks. Each chunk is with a TypeID or OS Type followed by a 32-bit integer specifying the size of the following data. Chunks can hold different data types like text, numerical data or raw data. Examples of AIFF based file formats are 8SVX (audio) AIFF (audio), ANIM(animation), DOC (pre Word97 text), IILBM (Raster image)
MIDI –MIDI files are textual files which contains instruction on how to playa piece of music.The actual music is generated from a digital synthesizer chip whichcan recognize the instructions and retrieve corresponding audiosamples using a repository of sounds.These files are very compact in size and ideal for web applications.AU –This is developed by Sun Microsystems.This audio file format consists of a header of six 32-bit words whichdefines the metadata about the actual audio data following it.There are 6 numbers defining the file type:oWord 0 is an identifier defining the file type,oWord 1 is a data offset value,oWord 2 is the data size in bytes,oWord 3 is the data encoding format,oWord 4 is the number of samples per second ,oWord 5 indicates the number of channels.
• MP3 – It is highly compressed audio format providing almost CD-quality sound. MP3 can compress a song into 5MBfor which it is extensively used for putting audio content on the internet. The file can be coded at a variety of bit rates and provides good results at bit rates of 96 kbps. The coding scheme does not provide any error correction or encryption.VOC- It is used for Sound Blaster Sound Cards. Sound upto 16bit stereo is supported along the compressed formats.
• RMF – Beatnik is a software based high performance music and audio playback technology created by Beatnik Inc. Beatnik Inc. developed their own audio file format called Rich Music Format (RMF)MP3Pro – It is an extended MP3 version from coding Technologies that uses Spectral Band Replication (SBR) in order to increase its efficiency for bit rates below 96 kbps/stero. MP3Pro has been implemented in only a few software and hardware products like Thomson demo player, Nero etc.
• WMA – It is a proprietary compressed audio file format used by Microsoft. It is a part of Windows Media framework. WMA is always encapsulated in an Advanced systems Format (ASP) file. The resulting file may have the filename suffix “vma” or “asf” with the “wma” suffix being used only if the file is strictly audio files in this format can be played using Windows Media Player,Winamp and many other alternative media players.
• RA – It is developed by RealNetworks. It is designed to conform to low bandwidths and it can be used as a stream audio format ie it can be played at the same time as it is downloaded. Many radio stations use Real Audio to stream their programing over the Internet in real time. The file extention of RA is ra,.rm or ram. The main player for RealAudio content is RealNetworks , RealPlayer.
Video File FormatThe various video file format are :I.AVI (Audio/Video Interleaved)II.MPEG (Motion Picture Expert Group)III.Real VideoIV.CinepackV.Windows Media Video (WMV)AVIThe native video file format on the Windows platform is AVT or audio-video interleaved.The name implies that in the same file both audio and video media is stored , since a video clipcan contain both types of media.The term interleaved means tht within the file the video data and the corresponding audio dataare kept in small chunks instead of widely separate blocks.AVI is an un-compressed format, ie the image frames and audio are stored without any type ofcompression and hence the sizes of AVI files could be large.An AVI file is played both on Windows by using the Windows Media Player or by a WebBrowser.
MOVThe Quick Time movie format is developed byApple for both the Windows and the Macintoshplatforms.These have an extension MOV and requires aprogram called Movie Player for playback, which isfreely downloadable from the Apple website.MOV is a compressed format and supports anumber of CODECs.It is widely used by web developers to createcross-platform video clips that can be downloadedfrom the Internet.
MPEGThe MPEG file format developed by the Moving PicturesExperts Group is a compressed format based on both intra-frame and inter-frame compression.There are several versions of MPEG:I.MPEG-1 – is designed for CD-ROM based applications andVideo-CDs and provides a quality comparable to VHS quality.II.MPEG-2 – is designed for DVD applications and provides aquality comparable to SVHS quality.III.MPEG-4- provides an efficient methods of object-orientedcontent based storage and retrieval of multimedia content.IV.MPEG-7- is a scheme for description of the multimediacontent through a set of standardized descriptors so thatmedia objects may be retrieved using queries.
REAL VIDEOThe RM file format was developed by RealNetworks for playing video files form WebPages.It supports streaming which means that thevideo file starts playing even before they aredownloaded from the Internet.A program called Real Player is required toplay back a RM file which is freely downloadablefrom the Real Networks web site.
CINEPAKCINEPAK was originally developed to play small movieson 386 and 030 systems from a single-speed CD-ROMdrive.Its greatest advantage is its extremely low CPUrequirements.Developers are using CINEPAK at higher data rates thanit was originally designed for and making ever-largermovies.VDO LIVEVDOLive is a architecture for web video deliverycreated by VDOnet corporation VDOLive is a server-based,”true steaming” architecture that actually adjuststo viewers connections as they watch movies.VDOLive’s true streaming approach differs fromQuicktime’s progressive download approach.
WMV-It is a set of proprietary streaming video technologiesdeveloped by Microsoft and part of the Windows MediaFramework.The Windows Media Audio format is used for audio track.Some third party players like Mplayer for Linux can also playback WMV files.WMV also implements digital rights management facilitiesMicrosoft has submitted version 9 of the WMV CODEC to theSociety for Motion Pictures and Television Engineers forapproval as an international standard.
Unit V Compression and Coding• The different types of media used in multimedia applications are text, fax, images, speech, audio and video are represented in digital form.• These different applications in multimedia need different storage capacity.• Since the space needed increases according to different applications it is difficult to store and transfer such data.• Following are the difficulties in possessing such data:I. Since their size is huge, storage requirements increases with multiple media files due to which there increases in the cost.II. Even if there is sufficient storage space such files require a large data transfer rate that may be beyond the capabilities of both the processor and hard disk.Due to these facts it is necessary to subject the media files to a process called compression.Compression reduces their file sizes using mathematical algorithms after which it becomes much easier to manipulate these files.The amount of compression which can be achieved depends both on the original media data as well as the compression technique applied.
Need FOR Compression• Compression is the key to the future expansion of the web, it’s the key to the increasingly use of multimedia and 3-D technology.• When multimedia data objects like binary document images, grey scale images, color images, photographic or video images , animated images, full- motion video etc are digitized large volume of data are generated.• Since every bit incurs a cost when stored, retrieved, transmitted and displayed.• The data objects requires a large amount of data storage due to which the access time for retrieving data increases.• In order to manage large multimedia data objects efficiently these data objects need to be compressed to reduce the file size for the storage of these objects.• The goal of data compression is to represent an information source as accurately as possible using the fewest number of bits.• Thus the compression techniques compresses the data which becomes easy to store, cost is reduced to store the large data.
Types of Compression• The two types of compression are Lossy and Lossless compression.Lossless data compression It makes use of data compression algorithms that allows the exact original data to be reconstructed from the compressed data. Examples are executable programs and source code. Some image file formats like PNG use only lossless compression and GIF uses a lossless compression method. In lossless compression data is not altered or lost in the process of compression or decompression. Decompression generates an exact replica of the original objects. Lossless compression technique is good for text data and for repetitive data in images like binary images and grey scale images. Lossless compression techniques have been able to achieve reduction in size in the range of 1/10 to 1/50 of the original uncompressed size without visibility affecting image quality.
Lossy CompressionWhen compression methods are used that may result in loss of someamount of information the key issue is the effect of this loss.Lossy compression is often used for compressing audio, grey scale or colorimages and video objects in which absolute data accuracy is not essential.Gray scale or color image are known as continuous tone images.When a video image is decompressed on a frame by frame basis the loss ofdata in one frame will not be perceived by the eye.In all cases there is usually a time factor that helps reduce the loss ofinformation. Lossy compression technique can be used alone or in combination withother compression methods in a multimedia objects consisting of audio, colorimages and video as well as other specialized data types.Some lossy compression mechanisms are:1.Joint Photographic Experts Group (JPEG)2.Moving Picture Experts Group (MPEG)3.Intel DVI4.Factals
Lossy versus Lossless TechniuqeI. A lossy method can produce much smaller compressed file than any known lossless method .II. Lossy methods are most often used for compressing sound, images or videos.III. The compression ratio of lossy video codecs are nearly always far superior to those of the audio and still-images.IV. Audio can be compressed at 10:1 with no noticeable loss of quality.V. Video can be compressed immensely with little visible quality loss e.g. 300:1.VI. When a user acquires a lossy-compressed file the retrieved file can be quite different from the original at the bit level while being in distinguishable to the human ear or eye for most practical purposes.
I. Lossless compression algorithms usually exploit statistical redundancy in such a way as to represent the sender’s data more concisely.II. Lossless compression is possible because most real-world data has statistical redundancy.III. Lossless compression schemes are reversible so that the original data can be reconstructed .IV. Lossless data compression algorithms will always fail to compress some files.V. Attempts to compress data that has been compressed already will result in an expansion.
Video Compression Techniques SIMPLE PREDICTIVE TRANSFORM Truncation INTERPOLATIVE DPCM STATISTICAL DCT CLUT SUSAMPLE MOTION HUFFMANRUN-LENGTH COMP FIXED ADAPTIVE COLOR VIDEO BIT COMPONENTS COMPRESSION ASSIGNMENT ALGORITHM
• In video compression the word technique refers to a single method of compression .• Algorithm refers to the collection of all the techniques used by any particular video compression system.• The block diagram above explains how techniques are used to create an algorithm.• Most compression systems will deal with the color components separately, processing each one by itself.• In decompression the components similarly are separately recovered and then combined into the appropriate display format after decompression.• The output of a compression process is a bit stream it is usually no longer a bitmap and individual pixels may not be recognizable.• The structure of the bit stream is important because it can also affect the compression efficiency and the behaviour of the system when errors occur in transmission or storage.• In the above diagram the separate box called bit assignment is where the bit stream structure is imposed on the compressed data.
Various video compression techniques are:1)Simple compression techniuqe2)Interpolative compression technique3)Predictive compression technique4)Transform compression technique5)Statistical compression techniqueSimple Video Compression techniques -This compression technique has three typesI.TruncationII.ClutIII.Run length
Truncation –•In truncation the data is reduced by lowering of•the bits pixel.•This is done by removing away some of the least significantbits for every pixel.•If truncation removes major information pixel thencontouring occurs and image will start looking like cartoon.CLUT – Color Lookup Table•It is a mechanism used to transform a range of input colorsinto another range of colors.•It can be a hardware device built into an imaging system or asoftware function built into an image processing application.•The hardware color look-up table will convert the logicalcolor numbers stored in each pixel of video memory intophysical color normally represented as RGB triplets that canbe displayed on a computer monitor.
• The palette is simply a block of fast RAM which is addressed by the logical color and whose output is split into the red, green and blue levels which drive the actual display.Run Length Encoding• In this technique blocks of repeated pixels are replaced with a single value and a count of how many times the repeat that value.• It works well on images which have areas of solid colors example – computer generated images , cartoons or CLUT images.• Depending on the kind of image the RL coding can achieve large amount of compression but effectiveness is limited to image that contain large amount of repeated values.
2) Interpolative Compression Technique –•In this the compression is done only on thechrominance part of the image while theluminance part is not interpolated.3) Predictive Compression Technique –•In this compression technique only that part istransmitted which is different as we havepredicted the part that is same .•Different predictive techniques are : PCM,DPCM and ADPCM.
Transform-•In transform coding compression technique it isa process that converts a bundle of data into analternate form which is more convenient forsome particular purpose.Statistical –•Statistical coding takes the advantage of thedistribution of the pixels values of an image.
JPEGThe JPEG standard was designed to provide acommon methodology for compression ofcontinuous-tone images i.e for images notrestricted to dual-tone only.This standard allows compressed files for gray-scale images, photographic images and stillvideo which can be utilized by variousmultimedia storage and communicationapplications.
JPEG Compression Technique• The most common accepted single-frame image compression is JPEG.• JPEG consists of a minimum implementation which are required to support various extension for specific applications.• JPEG compressor chips and PC boards are available to speed up the compression/decompression operation.• JPEG compression algorithms involves eliminating redundant data.• The amount of loss is determined by the compression ratio about 16:1 with no visible degradation.• JPEG compression involves several processing stages, starting with an image from a camera or other video source.• The image frame consists of three 2-D patterns of pixels, one for luminance and tow for chrominance. As the human eye is less sensitive to high-frequency color information, JPEG calls for the coding of chrominance information at a reduced resolution compared to the luminance information.• In the pixel format there is usually a large amount of low-spatial-frequency information and relatively small amounts of high-frequency information.• The image information is then transformed from the pixel domain to the frequency domain by a discrete cosine transform, a DSP algorithm similar to the fast Fourier transform.• This produces two-dimensional spatial-frequency components many of which will be zero and discarded.• Near zero components are truncated to zero and need not be sent on either.• JPEG while designed for still images is often applied to moving images or video.• Motion JPEG is possible if the compression/decompression algorithm is executed fast enough to keep up with the video data stream, but at typical compression ratios of about 16:1.